CODEWITHSUNDEEP
pythonarraysfunction
nappingkid
nappingkid

Reputation: 175

python store function in array

N00b question, maybe.

I am new-ish to python, but I was wondering if it is possible to store a function in an array? I want to do an array multiplication, where the value of one array is multiplied by a function on a location of another array of functions. Or actually, the value of the first array is inserted in the function of the designated location. This should create a new array where the values are an outcome of the "multiplication".

>>> import numpy as np
>>> a = [[1, 0], [0, 1]]
>>> b = [[f(x), g(x)], [(h(x), f(x)]]
>>> np.dot(a, b)
array([[0, 1],
   [2, 0]])

Assuming that f(x), g(x) and h(x) are defined functions. In this case python will say that x is not defined. So far I know. However, I do not want to say, for example, f(a[0][1]), because I want to reuse array b and also be able to put the functions on random locations in the array.

In short I detect three questions:
- Is there a known way to have an array where the values are functions?
- If not, should I redefine an array function or write a new class for this? (how do I attack this problem?)
- If it is possible to create an array of functions, can I fill the 'function values' dynamically in the array (populate the array dynamically with functions) or can it only be static values?

like for example

b[0]=f(x)

And yes, I really want to do this with python.

Upvotes: 0

Views: 16600

Answers (3)

Adirio
Adirio

Reputation: 5286

Is there a known way to have an array where the values are functions?

There is, as stated by others already.

def my func(x):
    return x

my_other_func = lambda x: x

l = [my_func, my_other_func]

If not, should I redefine an array function or write a new class for this? (how do I attack this problem?)

Not relevant

If it is possible to create an array of functions, can I fill the 'function values' dynamically in the array (populate the array dynamically with functions) or can it only be static values?

The 'function values' are called parameters and can be assigned after having the function in the array:

a[0](5)       # == my_func(5)
a[1]('Hello') # == my_other_func('Hello')

The problem is that you are trying to use matrix multiplication as parameter passing and that will not work, you could create a helper fucntion that does it.

def callByElements(parameterMatrix, functionMatrix):
    rows = len(parameterMatrix)
    cols = len(parameterMatrix[0])
    result = np.zeros( (rows, cols) )
    for i in range(rows):
        for j in range(cols):
            result[i,j] = functionMatrix[i,j](parameterMatrix[i,j])
    return result

Upvotes: 1

Scott Hunter
Scott Hunter

Reputation: 49803

Your example puts the result of calling a function into your array.

b[0] = f

actually puts the function itself into the array, so that

b[0](x)

would have the same effect as 

f(x)

Upvotes: 3

Axnyff
Axnyff

Reputation: 9944

f(x) is not a function (even in mathematics). The function is f. In python there is no problem to store functions in array:

def my_func():
    print("Foo")

my_other_func = lambda: print("Bar")

my_arr = [my_func, my_other_func]

Upvotes: 4

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